Trait Cast

pub trait Cast: ObjectType {
    // Provided methods
    fn upcast<T>(self) -> T
       where T: ObjectType,
             Self: IsA<T> { ... }
    fn upcast_ref<T>(&self) -> &T
       where T: ObjectType,
             Self: IsA<T> { ... }
    fn downcast<T>(self) -> Result<T, Self>
       where T: ObjectType,
             Self: CanDowncast<T> { ... }
    fn downcast_ref<T>(&self) -> Option<&T>
       where T: ObjectType,
             Self: CanDowncast<T> { ... }
    fn dynamic_cast<T>(self) -> Result<T, Self>
       where T: ObjectType { ... }
    fn dynamic_cast_ref<T>(&self) -> Option<&T>
       where T: ObjectType { ... }
    unsafe fn unsafe_cast<T>(self) -> T
       where T: ObjectType { ... }
    unsafe fn unsafe_cast_ref<T>(&self) -> &T
       where T: ObjectType { ... }
}

Upcasting and downcasting support.

Provides conversions up and down the class hierarchy tree.

Provided Methods

fn upcast<T>(self) -> T

where T: ObjectType, Self: IsA<T>,

Upcasts an object to a superclass or interface T.

NOTE: This statically checks at compile-time if casting is possible. It is not always known at compile-time, whether a specific object implements an interface or not, in which case upcast would fail to compile. dynamic_cast can be used in these circumstances, which is checking the types at runtime.

Example

let button = gtk::Button::new();
let widget = button.upcast::<gtk::Widget>();

fn upcast_ref<T>(&self) -> &T

where T: ObjectType, Self: IsA<T>,

Upcasts an object to a reference of its superclass or interface T.

NOTE: This statically checks at compile-time if casting is possible. It is not always known at compile-time, whether a specific object implements an interface or not, in which case upcast would fail to compile. dynamic_cast can be used in these circumstances, which is checking the types at runtime.

Example

let button = gtk::Button::new();
let widget = button.upcast_ref::<gtk::Widget>();

fn downcast<T>(self) -> Result<T, Self>

where T: ObjectType, Self: CanDowncast<T>,

Tries to downcast to a subclass or interface implementor T.

Returns Ok(T) if the object is an instance of T and Err(self) otherwise.

NOTE: This statically checks at compile-time if casting is possible. It is not always known at compile-time, whether a specific object implements an interface or not, in which case upcast would fail to compile. dynamic_cast can be used in these circumstances, which is checking the types at runtime.

Example

let button = gtk::Button::new();
let widget = button.upcast::<gtk::Widget>();
assert!(widget.downcast::<gtk::Button>().is_ok());

fn downcast_ref<T>(&self) -> Option<&T>

where T: ObjectType, Self: CanDowncast<T>,

Tries to downcast to a reference of its subclass or interface implementor T.

Returns Some(T) if the object is an instance of T and None otherwise.

NOTE: This statically checks at compile-time if casting is possible. It is not always known at compile-time, whether a specific object implements an interface or not, in which case upcast would fail to compile. dynamic_cast can be used in these circumstances, which is checking the types at runtime.

Example

let button = gtk::Button::new();
let widget = button.upcast::<gtk::Widget>();
assert!(widget.downcast_ref::<gtk::Button>().is_some());

fn dynamic_cast<T>(self) -> Result<T, Self>

where T: ObjectType,

Tries to cast to an object of type T. This handles upcasting, downcasting and casting between interface and interface implementors. All checks are performed at runtime, while downcast and upcast will do many checks at compile-time already.

It is not always known at compile-time, whether a specific object implements an interface or not, and checking as to be performed at runtime.

Returns Ok(T) if the object is an instance of T and Err(self) otherwise.

Example

let button = gtk::Button::new();
let widget = button.dynamic_cast::<gtk::Widget>();
assert!(widget.is_ok());
let widget = widget.unwrap();
assert!(widget.dynamic_cast::<gtk::Button>().is_ok());

fn dynamic_cast_ref<T>(&self) -> Option<&T>

where T: ObjectType,

Tries to cast to reference to an object of type T. This handles upcasting, downcasting and casting between interface and interface implementors. All checks are performed at runtime, while downcast and upcast will do many checks at compile-time already.

It is not always known at compile-time, whether a specific object implements an interface or not, and checking as to be performed at runtime.

Returns Some(T) if the object is an instance of T and None otherwise.

Example

let button = gtk::Button::new();
let widget = button.dynamic_cast_ref::<gtk::Widget>();
assert!(widget.is_some());
let widget = widget.unwrap();
assert!(widget.dynamic_cast_ref::<gtk::Button>().is_some());

unsafe fn unsafe_cast<T>(self) -> T

where T: ObjectType,

Casts to T unconditionally.

Panics if compiled with debug_assertions and the instance doesn’t implement T.

unsafe fn unsafe_cast_ref<T>(&self) -> &T

where T: ObjectType,

Casts to &T unconditionally.

Panics if compiled with debug_assertions and the instance doesn’t implement T.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementors

impl<T> Cast for T

where T: ObjectType,